staging: rtl8712: constify usb_device_id

usb_device_id are not supposed to change at runtime. All functions
working with usb_device_id provided by <linux/usb.h> work with
const usb_device_id. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/usb_intf.c

@@ -47,7 +47,7 @@ static int r871xu_drv_init(struct usb_interface *pusb_intf,
 
 static void r871xu_dev_remove(struct usb_interface *pusb_intf);
 
-static struct usb_device_id rtl871x_usb_id_tbl[] = {
+static const struct usb_device_id rtl871x_usb_id_tbl[] = {
 
 /* RTL8188SU */
 	/* Realtek */